The present invention relates in general to a portable light source unit which is particularly suited for simulating a fire to test the operation of fire detectors.
Hydrogen fires present a significant danger during rocket launch preparations at the Kennedy Space Center. These types of fires are particularly hazardous if they occur during daylight hours because hydrogen burns with a flame that is virtually invisible to the naked eye. As a result of this potential hazard, the Kennedy Space Center has installed groups of special detectors at each launch pad which can detect the presence of a hydrogen fire. These detectors are specifically shortwave ultraviolet (UV) detectors which utilize a Hamamatsu ultraviolet detector tube to indicate the presence of radiation in the optical wavelength range from 180 nm to 240 nm. This spectral window is unique for within it, a hydrogen fire emits a small amount of radiation, while incandescent lamps and the sun emit no significant radiation, and the air is transmissive. Consequently, this spectral region is very favorable for monitoring hydrogen fires in air with a minimum possibility of false alarms.
Each launch pad utilizes about 60 hydrogen fire detectors in one of three configurations referred to as (-1), (-2) and (-3). A (-2) unit has an unmodified configuration designed to alarm off of a standard hydrogen fire (defined as the fire produced by burning H.sub.2 flowing at 5 SLPM through a 1/16" orifice) at a distance of 24 feet. A (-1) unit is a (-2) unit with a screen mesh added to reduce sensitivity to the point where the unit will alarm off of a standard hydrogen fire at 15 feet. A (-3) unit has modified electronics added to increase the sensitivity such that it will alarm at a distance of 54 feet from a standard hydrogen fire.
Before flowing hydrogen at a launch pad, operations personnel check the performance of the hydrogen fire detectors with a hydrogen fire simulation device. In the past, the simulation devices have been simply a flashlight with an ultraviolet light source that emits UV radiation in the 180 nm to 240 nm wavelength range. To check the performance of the detectors, the operations person stands as close as is reasonable to the fire detector and aims the flashlight at it. If the detector unit alarms, the unit is considered operational, and if it does not, the unit is declared defective and is replaced.
This testing approach has two primary problems. First, the flashlight has no intensity adjustment and emits enough radiation to alarm the least sensitive (-1) unit at the maximum distance required, which is 50 feet. This is sufficient to cause some of the more sensitive (-2) units to arc and latch in an alarm state for up to 30 minutes when exposed at close distances. Second, the bulb intensity is never calibrated so the user has no method to determine whether a given bulb is deteriorating over time, or if a new bulb has a dramatically different emission intensity than an old bulb. This results in the likelihood that the performance of a detector will not be properly assessed if the bulb intensity changes significantly over time.